1. Field of the Invention
This invention relates generally to an apparatus for treating malignant tumors, and, more specifically, to metal seeds that are implanted by injection into tumorous tissue for simultaneous application of thermal energy and radioactive emissions to such tissue.
2. Description of the Related Art
In a journal article entitled xe2x80x9cPractical Aspects of Ferro-magnetic Thermoseed Hyperthermia,xe2x80x9d published in the Radiologic Clinic of North America, Vol. 27, No. 3, dated May 1989, Ivan A. Brezovich and Ruby F. Meredith, both with the University of Alabama at Birmingham, presented a general treatise on a method of treating tumors by interstitially implanting small pieces of ferromagnetic alloy wire into the tissue and then exposing the subject to an externally applied, oscillating, magnetic field of a predetermined frequency and field strength so as to cause inductive heating of the thermoseeds within the body. This paper points out that by selecting a ferromagnetic material having a suitable Curie point, such a thermoseed becomes self-regulating when the temperature of the seed approaches the Curie point, at which temperature the material becomes non-magnetic. The Carter U.S. Pat. No. 5,133,710 relates to the same technology.
The Paulus et al., U.S. Pat. No. 5,429,583, which is assigned to the assignee of the present application, describes the use of a palladium-cobalt (Pdxe2x80x94Co) alloy as an improved material for such thermoseeds. By properly adjusting the percent by weight of Pd and Co in the alloy, a Curie point temperature (between 40 C. and 100 C.) can be chosen that lies within a range of therapeutic temperatures. Upon exposure to an oscillating magnetic field, the temperature of the thermoseed is self-regulating. The temperature increases until the Curie temperature is reached, at which point, the material becomes non-magnetic, and no additional heating occurs.
It is also known in the art that seeds to be implanted in tumorous tissue can be coated or otherwise treated so as to emit ionizing radiation effective in killing cancerous tissue without excessive damage to surrounding healthy tissue. In this regard, reference is made to Kubiatowicz U.S. Pat. No. 4,323,055, Russell, Jr. et al. U.S. Pat. Nos. 4,702,228 and 4,784,116, Suthanthiran U.S. Pat. No. 4,891,165 and Carden Jr. U.S. Pat. No. 5,405,309, each of which describes techniques for making and utilizing radioactive seed implants and are incorporated by reference herein.
For more than a decade, medical investigators have discussed the synergy of hyperthermia and ionizing radiation in the treatment of several types of tumors. The synergism is believed to be due to some form of combined damage on a cellular level, but increasingly, investigators are theorizing that the increase in blood flow during hyperthermia facilitates the radiation dose by lowering the percentage of hypoxic cells in the tumor. It has been widely known that poorly oxygenated tumors are much more resistant to ionizing radiation than normally oxygenated cell populations. Before the patents cited above, no one appears to have disclosed a combination implant that could produce both thermal and ionizing radiations simultaneously. An implant capable of delivering truly simultaneous thermal and ionizing radiation was a unique advancement, as most clinical research in this area had used separate therapies spaced as close together as possible. The present invention provides just that type of desired implant.
The combination of ionizing radiation and thermal radiation in the seed implants of the related patents cited above offers the further advantage that even when the ionizing radiation given off by the implants has been virtually expended, the magnetic properties of the implants remain intact, allowing for continued hyperthermia or ablation therapy. In normal brachytherapy seeds, after the ionizing radiation has dissipated, the implants are completely inert and have no therapeutic value whatsoever.
The present invention provides an improved implantable seed device, a method of producing the seed and a method of treating a patient with the seed wherein radioactive pellets with sufficient source strength are positioned under encapsulation at least at the ends of the seed and preferably at intervals along the seed providing several improvements over the prior art, as will be discussed below.
The present invention provides implantable seeds for treating soft tumorous tissue. The seeds comprise rod-shaped ferromagnetic alloy elements with end caps configured as hollow tubes that are closed on one end and open on the other end and contain radioactive pellets and optional spacers. The implantable seeds can further comprise hollow tubular sleeves that connect a series of ferromagnetic alloy elements and also contain radioactive pellets and optional spacers therein. The ferromagnetic alloy may be palladium-cobalt (Pdxe2x80x94Co) with a Curie temperature between about 40 C. and 100 C., and the end caps and tubular sleeves may be made of titanium. The radioactive pellets may comprise palladium-103 or iodine-125. Preferably each Pdxe2x80x94Co element comprises one piece of solid material.
In another embodiment the rod-shaped ferromagnetic element has at least one axially-extending channel along its outer surface. A radioactive source is configured to fit into the channel, and an outer tubular sleeve is positioned coaxially over the rod-shaped ferromagnetic element, thus holding the radioactive source in place.
Another aspect of the present invention provides a method of making an implantable seed for supplying thermal and ionizing radiation to cancerous tissue, comprising providing at least one rod-shaped ferromagnetic alloy element with radioactive sources held in place adjacent to the ends of the element(s) with cylindrical tubes. An external oscillating magnetic field is supplied to act on the ferromagnetic alloy element(s) to produce heat therein. The ferromagnetic alloy may be palladium-cobalt. Preferably the oscillating magnetic field has a maximum flux density of between 25 gauss and 100 gauss and a frequency between 25 kHz and 200 kHz.
Another aspect of the present invention provides a method of treating a patient comprising positioning a plurality of implantable seeds in cancerous tissue so that the longitudinal axes of the seeds are aligned substantially in parallel. The seeds comprise a ferromagnetic material, such as Pdxe2x80x94Co, whose Curie point temperature is in a therapeutic range, preferably between 40 C. and 100 C. Heat is provided by exposing the implantable seeds to an external oscillating magnetic field aligned generally parallel to the longitudinal axes of the implantable seeds. Ionizing radiation is provided from radioactive sources, such as palladium-103 or iodine-125, positioned in cavities enclosed by end caps attached over the ends of the implantable seeds. Additional ionizing radiation may be provided from radioactive sources positioned in cavities within hollow, tubular sleeves that connect adjacent sections of each implantable seed. The spacing between the radioactive sources may be chosen to provide a uniform or predetermined non-uniform dose profile around each implantable seed. Preferably the implantable seeds are exposed to the oscillating magnetic field in a plurality of sessions over a course of treatment, the length of which will be related to the half-life of the radioactive sources.
Further features and advantages of the present invention will become apparent to those of ordinary skill in the art in view of the detailed description of preferred embodiments below, when considered together with the attached drawings and claims.